Current Committees

Biochemistry Program

Neuroscience Program

Research

In the Lebestky lab, we utilize the genetic model system of Drosophila melanogaster for the study of behavioral genetics and molecular neurobiology techniques to understand arousal and sensory integration. Animals use their senses to learn about their immediate environment, parse the relevant information, and react in a meaningful way. If the sensory inputs are not interpreted correctly, this can cause inappropriate reactions, such as exaggerated behavioral responses to innocuous non-threatening stimuli, or by not reacting strongly enough to real threats. These concepts also translate into human biology, as imbalances in arousal and sensory gating are linked to pathologies, such as insomnia, attentional disorders, autism, and anxiety.

Behavioral Gating Mechanisms and Dopaminergic Circuitry in Arousal

My lab has used the mechanical startle assay to identify the Dopamine Receptor (DopR) as an important component of the gating mechanism for “stress-based” arousal in the Central Complex region of the brain (blue circle) and we will extend the analysis to more deeply investigate the role of Dopaminergic circuits as well as try to identify and characterize additional molecular components. Mammalian studies of the basal ganglia suggest that DA oppositely regulates locomotion based on separate subclasses of post-synaptic neurons, also implicating the complex relationships between D1 and D2 family DA receptors. However, nothing is known of the interplay between these type I and II receptor families in Drosophila, and our behavioral assays allow for precise functional characterization and analyses currently unavailable in mammalian systems. To investigate these interactions in Drosophila, we will use multiple molecular, genetic, and behavioral techniques to separate and compare different forms of dopaminergic signaling in the brain. By coupling functional circuit manipulations with traditional immunohistochemical imaging techniques, we will try to unlock the many functions of multiple brain regions and evaluate our insights for relevant comparative studies of higher vertebrates.

Sensory Integration of Vision and Arousal State

There are very few examples of well-defined circuitries and molecular mechanisms in any model system, for the integration of arousal state and output behaviors. Therefore, in order to understand how arousal states translate into modulation of a simple sensory-based behavior, we use “the fly stampede” that measures visual responses to motion by tracking walking behavior. The arena of LED arrays create a pattern of moving light bars that elicit rapid reflexive walking behaviors in a freely moving population of flies. Furthermore, visual stimuli can be modulated to drive locomotor responses towards either the middle, or the ends of the arena. It was anecdotally noted in preliminary experiments that the fidelity and magnitude of the locomotor response is largely dependent on the animals’ arousal state, since animals that receive no mechanical startle prior to the visual stimuli perform poorly in responding to motion. Also, given my earlier analysis of arousal phenotypes of DopR mutants, we have tested their performance in the visual arena, and these mutant animals are indeed compromised in their ability to perform visual tasks. The visual system in Drosophila is well characterized and the extensive control of both stimuli parameters and genetic manipulation of

specific cell types allows exact precise separability of potential hypotheses. We will functionally dissect the circuit requirements for DopR in vision and arousal by utilizing Gal4 lines as performed previously for separating sleep/wake and startle-based arousal (Figure in section I). These studies, coupled with new genetic screens, may provide new candidates and methods for understanding the molecular nature of disorders involving regulation of impulsive motor behaviors due to altered attentional or arousal states.

The Role of Serotonin in OCD and Autism

The primary molecular target for pharmacological treatment of depression and anxiety disorders is the human Serotonin Transporter (hSERT/SLC6A4). However, the mechanisms as to how blockade of hSERT results in therapeutic changes are not known. Human genetic studies have identified risk alleles that can provide critical clues about the molecular pathways responsible for disease. Moreover, the replication of these alleles in model organisms allows the experimental study of their activity in vivo, and testing of therapeutic strategies to mitigate their pathophysiological effects. Several highly conserved residues in SERT have been shown to be critical for its subcellular localization, and mutation of these sites may contribute to both obsessive-compulsive disorder (OCD) and autism. dSERT transgenes containing identical SERT mutations of interest can be used to test their ability to rescue the phenotype of a dSERT null mutant allele. Additionally, genetic model organisms such as Drosophila are highly amenable to directed genetic interaction studies and large-scale genetic screens. Such strategies may identify compensatory mutations that reduce the pathophysiological effects of the risk alleles, and help determine the cellular pathways required for the normal function of hSERT.